The invention relates to release liner base stocks which are used as a carrier web to dispense die cut film labels onto glass and plastic bottles. More particularly, there is disclosed a non-curling release liner and base stock which acts as a carrier for printed films and labels. The release liner is wound up and discarded at the end of the labelling process.
The current release liner on the market consists of a substrate material such as an unbleached kraft type paper and extrusion coated thereon a layer of a polymer resin. The polymer layer, which has been coated onto the paper, is then coated with a silicone type material which acts as the release layer for a subsequently attached label or printed film. The release liner and a film sandwich material or label is then sent to a printer, that prints on the film in roll form. The film sandwich material is comprised of a printed film and an adhesive. The final step is for rolls, of the assembled laminate, release liner and printed film sandwich or label, to be die cut and dispensed onto bottles or the like. The die cut is made through the film, the adhesive, and partly into the polymer coating layer. The release liner acts as a carrier for the film labels or printed film sandwich, and is wound up and discarded at the end of the labelling process.
A problem with the existing release liner laminate is that loose fibers from the paper side of the laminate get picked off and contaminate the polymer layer and printed film or label layer surfaces during silicone coating, adhesive laminating, and printing operations. Manufacturing machines used for the process have to be taken out of production to manually clean the paper fiber from coating and printing cylinders.
Another problem with the current release liner laminate is that during the adhesive laminating step, the heat that is supplied to the web causes the liner to curl in the cross machine direction due to shrinkage of the polymer coating. To eliminate this curl, water or steam has been applied to the paper side of the sheet. This application is an expensive and inefficient added step to the process.
One object of the present invention is to reduce the fiber contamination problem by applying a specialized coating to the uncoated side of the paper substrate of the release liner. The specialized coating covers and protects the paper fibers. This coating also significantly reduces the amount of curl in the liner, thereby significantly reducing the amount of steam that needs to be applied to the sheet during the adhesive lamination process.
Another object of the invention is to improve the efficiency of coating, laminating, and printing equipment by significantly reducing fiber pick-off contamination from the uncoated side of the paper substrate of the release liner.
A further object of the present invention is the reduction of cross-directional curl of the liner paper.